This might or might of be the case with the original PD, but I recall Google removed a number of apps from the store that failed to keep up with targeting a minimum Android API version number. Could be thwt dev didn’t respond to the alerts from Play Store and the app got removed as part of that purge. I think that happened about the time you mentioned in your post.

I could convince myself there was some discussion about it on the pixeldungeon sub over at the Old Place, but honestly I never played the original version anymore and didn’t really pay attention.

Of course I could also be totally mistaken, so don’t quote me on any of that